Thread: Photons

If Photons have no mass; then how come they are affected by gravity ?

Although photons have no mass, they have energy E=h*f
where: h is Planck's constant and f is the frequency of the photon.
Einstein showed that mass and energy are equivalent.
So we know that if sth has mass,it is affected by gravity.
Now we can add: if sth has energy,it is affected by gravity because mass and energy are equivalent.

''You could also imagine gravity,as curvatrure of spacetime (Einstein).This way it is clear that even massless particles are affected by gravity''

Who said photons are 'attracted by gravity? - they are not, what happens is gravity 'bends' space, but light travels in a straight line. it is space that is curved - it only appears to us that light 'bends' because our tiny minds are a dimension short of a full set.

I see what you mean about the curvature of space; but I was referring to the fact that photons cannot escape the gravity of a black-hole. If they were truly massless then why is there a speed restriction to 186,000 miles per second. Surely if they were masless, their speed would be infinate ?

Okay..........erm.......Logic tells me then that if as you say both energy and mass are equivelant and that if a photon has no mass then for it to exist at all, it must have infinate energy ?

Originally Posted by leohopkins

I see what you mean about the curvature of space; but I was referring to the fact that photons cannot escape the gravity of a black-hole. If they were truly massless then why is there a speed restriction to 186,000 miles per second. Surely if they were masless, their speed would be infinate ?

this is why "nothing can travel faster than light", is thought.

i would like to know what could be in the BH to create light. however they "say", not even light to explain the intense gravity.

Originally Posted by leohopkins

Okay..........erm.......Logic tells me then that if as you say both energy and mass are equivelant and that if a photon has no mass then for it to exist at all, it must have infinate energy ?

energy is proportionate to mass. the more of one, the more of the other but always limited to each others.

Originally Posted by jackson33

i would like to know what could be in the BH to create light. however they "say", not even light to explain the intense gravity.

its not a matter of something in the black hole that makes light. When people say light can't even escape the gravity of a black hole they are talking about light generated outside of the black hole but tries to pass through. It goes in one side but can't escape the other.

Originally Posted by leohopkins

Okay..........erm.......Logic tells me then that if as you say both energy and mass are equivelant and that if a photon has no mass then for it to exist at all, it must have infinate energy ?

Jackson covered that pretty well. It is not that there is 100% of something to be divided by energy and mass, resulting in less of one equals more of the other. It actually is more of one equals more of the other.

Okay, more of one equals more of the mother as far as mass and energy are concerned. if this is the case then logically; zero mass would mean zero energy ?

shawn; anything entering the BH is not as it was, whatever that was. a star a major form of perceived light is shredded or disintegrates prior to being absorbed. there should be nothing inside this thing other than a dense mass of matter particles. what ever goes through has no light or anything large enough to reflect light. the observed horizon is matter thought to be leaving the area or not absorbed. no light can go out if none enters, certainly none we could see...

Okay, more of one equals more of the other as far as mass and energy are concerned. if this is the case then logically; zero mass would mean zero energy ?

Originally Posted by leohopkins

Okay, more of one equals more of the mother as far as mass and energy are concerned. if this is the case then logically; zero mass would mean zero energy ?

of course zero mass, zero energy is produced. we get our energy from the sun which is 99.80% of our solar systems mass and produces so much energy that our comparatively tiny planet receives such a small amount but is so effected.

Okay, so, photons have zero mass therefore zero energy. So then, if they have no energy; how do they travel at speed C. Surely anything that moves requires energy ?

Photon has zero REST mass and this leads to the speed c when travels.

if you say photon has zero energy, then such photon cannot exist as photon itself is a packet of energy.

btw, photon has zero REST mass but non-zero mass according to the principle of mass-energy equivalence (E=mc^2). So, we must state carefully what mass are tallking with (rest mass? relativistic mass?).

=)

How can a photon be at rest ?

Does anyone know what the (average-ish) speed of light through clear glass is ?

Originally Posted by leohopkins

How can a photon be at rest ?

Does anyone know what the (average-ish) speed of light through clear glass is ?

when you throw a ball, the ball has no energy but will travel until the energy you gave it is dispersed. the sun emits energy,( throws the ball) into no space which as no major source for this dispersement. when what little there is heading our way gets here it will be dispersed or absorbed.

you might "google" -electromagnetic energy- or scale to understand better what all is involved. light will travel through glass at C but look what happens is that glass is shaped, a lens or a magnifying piece. each has very different results...

Depends upon the type of glass - it can be as low as 66% if I remember correctly, incidentally in fibre optic cables there are several layers of glass each with it's own refractive index, the more from the centre the light strays the greater the refraction to 'correct' it. The greater the refractive index the more light is 'slowed down' and the greater the refractive angle.

Refractive Index = C/V

C = Speed of light[in a vacuum], V= Velocity in medium

Sorry Jackson33 your assertion that light travels through Glass at 'C' [ie 300MKm/s] is incorrect.

i figuerd photons was the quantified energy of electrons, and not particles?